Switch-case syntax

The switch-case statement in C++ is a control statement used to execute one block of code from multiple options based on the value of a variable or an expression. It provides an alternative to using multiple if-else statements and can make the code cleaner and more readable when dealing with multiple conditions.

Syntax

Here is the basic syntax of a switch-case statement in C++:

switch (expression) {
    case constant1:
        // code to be executed if expression == constant1
        break;
    case constant2:
        // code to be executed if expression == constant2
        break;
    // you can have any number of case statements
    default:
        // code to be executed if expression doesn't match any constant
}

Key Points

1. Expression: The switch statement evaluates an expression once and compares the result with the values of each case label.
2. Case Labels: Each case label must be a unique constant expression, typically integers or characters.
3. Break Statement: The break statement is used to exit from the switch block. If break is omitted, the execution will continue to the next case label (fall-through behavior).
4. Default Case: The default case is optional but recommended. It executes if none of the case labels match the expression. Think of it as a final else in an if-else chain.
5. Fall-through: If you do not use break at the end of a case, the execution will continue to the next case. This can be useful in some situations but should be used with caution.

Example

#include <iostream>

int main() {
    int day = 3;

    switch (day) {
        case 1:
            std::cout << "Monday\n";
            break;
        case 2:
            std::cout << "Tuesday\n";
            break;
        case 3:
            std::cout << "Wednesday\n";
            break;
        case 4:
            std::cout << "Thursday\n";
            break;
        case 5:
            std::cout << "Friday\n";
            break;
        case 6:
            std::cout << "Saturday\n";
            break;
        case 7:
            std::cout << "Sunday\n";
            break;
        default:
            std::cout << "Invalid day\n";
            break;
    }

    return 0;
}

Detailed Explanation

1. Expression Evaluation: In the example above, day is evaluated once.
2. Case Matching: The value of day is compared with each case label.
3. Case 3 Execution: Since day is 3, the code under case 3: is executed, printing “Wednesday”.
4. Break Statement: The break statement prevents the execution from falling through to case 4: and beyond.
5. Default Case: If day had a value other than 1 to 7, the default case would be executed, printing “Invalid day”.

Common Use Cases

• Menu Selection: Often used in console applications to handle user menu selections.
• State Machines: Used in implementing state machines where the program transitions between different states based on input.
• Command Handling: Handling different commands in command-line utilities or scripts.

Limitations

• Constant Expressions: The case labels must be constants known at compile time.
• Non-Continuous Values: Not suitable for ranges of values or conditions that aren’t based on discrete, constant values.
• Data Types: Typically used with integral or enumerated types. Using strings or floating-point numbers directly is not supported in standard C++.